I know nothing about mathlab. But from a transformer analysis point of view:
Xp and Xs should be combined.
Do modeling at no load and also at full load.
At no load Xp, Xs, Rp and Rs can be ignored.
At full load Rc and Xm can be ignored

Above simplification can be used for normal transformers. There are some extremely rare exceptions where the preceding is not true.

Some transformers engineers say Xp and Xs can not be combined. I am in the group that say they can be combined.